Solvent fractionation



l Patented Feb. 4, 1936 PATENT OFFICE SOLVENT FRACTIONATION George L. Parkhurst, Chicago, Ill., assignor to Standard Oil Company, Chicago, lll., a corporationof Indiana Application April 29, 1933, Serial No. 668,593 8 Claims.l (Cl. 196-37) This invention relates to the solvent fractionation of petroleum materials and particularly lubricating oils and lubricating oil stocks. It further relates to the combined solvent fractionation o! lubricating oils and naphthas.

It is an object of the invention to produce higher yields ofimproved lubricating oils than is possible by existing methods and/or to produce better products than do existing methods. The

lo objects of the invention will become apparent in detail as the description thereof proceeds.

. It has long been known to fractionate lubricating oil stocks by means of liquid sulfur dioxide. In these processes .the more desirable parafnic and naphthenic compounds are left undissolved and form the railinate, whereas the less desirable aromatic and oleiinic constituents are dissolved by the sulfur dioxide and form the ex-'- tract. The railinate fraction is, in general, 20 characterized by a lower temperature co-efiicient of viscosity, lower carbon forming tendency and greater sludge and oxidation stabilities than the original lubricating oil stock.

I have now found that these improved characteristics of the railinate are very materially enhanced by the addition to the liquid sulfur dioxide oflow boiling olenic hydrocarbons suchv as are contained in cracked petroleum naphthas and particularly in those petroleum naphthas pro- 30 duced by vapor phase cracking processes. By variations in operating conditions particularly temperature, composition of the mixed solvent and ratio of solvent to material being extracted, it is possible to utilize the advantages of 1 my proc- 35 ess either by producing a better rainate than can be done by means of liquid sulfur dioxide alone or alternatively produce a higher yield of rainate similar to that produced by prior art processes. The optimum operating conditions can be read- 40 ily determined by experiment in each particular case. My invention can best be described by reference to the accompanying drawing which represents a conventional ow diagram of a process for the .15 utilization of my invention. A petroleum material, preferably a lubricating oil stock, is introduced into mixer II by means of line I2. Simultaneously, a cracked naphtha, preferably produced by a vapor phase cracking process, is intro- '50 duced into mixer II through line I3. Liquid sulfur dioxide can also be introduced directly at this point but I prefer to introduce an extract fraction from a subsequent stage in the process. 'I'his fraction contains a high percentage of liquid sulfur dioxide and is introduced into mixer I I by means of line I4. These various materials can be cooled, either prior to or subsequent tovmixing, to the temperature'desiredfor the fractionation operation. Cooling means are not specically shown,-cooling may be eected by exchangers or 5 it may be obtained by the vaporization of a portion of the sulfur dioxide. The mixed materials from mixer II pass through line I5 into separator I6 wherein extract and ralnate fractions separate, the former being withdrawn through line Il and the latter through line I8. The extract fraction will be found to contain the undesirable' constituents of the lubricating oil stock. namely the naphthenic and aromatic constituents together ,with a naphtha fraction which has a high u antiknock value (high octane number) due to its high percentage of olenic constituents as compared with the portion of the original naphtha passing out of settler I6 through line i8.

The extract is withdrawn through line I1 by 20 means of pump I8 into bubble tower I9 wherein the lubricating oil constituents, naphtha constituents and sulfur dioxide are separated by frac-y tional distillation. The oil extract containing undesirable lubricating oil constituents is removed 25 from the bottom oi tower I8 through line 20 and valve 2 I. A steam coil 22 in the'base oi tower I8 provides reboiling and prevents the withdrawal of naphtha constituents at this point. At an intermediate level in the tower above the point at 30 which the extract is introduced, a special trapout plate 23 is provided and the condensate at that point is withdrawn through line 24 and introduced into stripping column 25, the gasoline constituents being withdrawn from the base oi 35 the stripping column by means of line 26. A small amount of reboiling may be provided by means of closed steam coil 21; Any sulfur dioxide in the material removed through linel 24 is returned to the main tower I9 by means of line 40 28. Cooling at the top of tower I9 is provided by means of dephlegmating coil 29. Sulfur dioxide passes off in vapor form from the top of the tower through linev 30, passes through compressor 3| and is cooled and/or condensed by means of cooling coil 32, passing into storage tank 33 in liquid form.

Returning to the rainate fraction removed from settler I8 by means of line I8 it is pumped (if necessary) by means of pump 34 into mixer 35, 50 at which point it is mixed with the extract iraction from the third stage of the process introduced through line 38. The mixed material passes through line 31 into a second settler 38, wherein extract and raflinate fractions are again formed. The former, is removed from separator 39 through valve 39', pump 40 and line I4 into mixer Il. A portion of the high octane number naphtha fraction from stripping tower can also be introduced at this point by means of line 4| and valve 42, the remainder being Withdrawn from the process through valve 43. By recycling at least a part of this high octane number naphtha fraction in which the olenic hydrocarbons present in the original naphtha stock have been concentrated it is possible to increase the olefine content of the naphtha present in the various stages of the process and thereby increase the efficiency of the solvent fractionation of the lubricating oil. By means of valves 42a and 42h it is also possible to increase in a direct manner the oleiinic hydrocarbon content of the mixed solvent present in the second and third stages, respectively.

'I'he ramnate from separator 38 which contains 'a higher grade of lubricating oil constituents than did the s' raiiinate from separator I6 is pumped (if necessary) by means of pump 44 into mixer 45, wherein it is mixed with fresh liquid sulfur dioxide introduced from storage tank 33 by means of pump 46. `The mixed materials pass through line 41 into a third separator 48 wherein extract and raffinate fractions are again formed. The former, containing an intermediate grade of lubricating oil constituents, is recycled by means of pump 49 to an intermediate point in the process, preferably to mixer preceding the second stage of the extraction. The raiiinate fraction from separator 48 contains lubricating oil constituents which have been extracted three times and which contain little or nothing except the highly desirable paraiiinic and in some instances, naphthenic constituents. 'I'his raiiinate is removed through line 50 by means of pump 5I and is introduced into bubble tower 52 which is generally similar to bubble tower I 9 and contains vtrap-out plate 53, dephlegmating coil 54 and reboiling coil 55 corresponding respectively to elements 23, 29 and 2i in tower I9. The rainate -from which gasoline constituents and sulfur dioxide have been removed is drawn off at the base of tower 52 through valve 56 and passes to' subsequent rening operations or to storage. Condensate is withdrawn from trap-out plate 53 into stripping column 51 corresponding to stripping column 25. The gasoline constituents are removed from the base of column 51 through valve 59. The naphtha fraction removed at this point is a relatively paralnic fraction and is characterized by a low octane number. It may be used -as a low grade gasoline or as a special naphtha or it may be subjected to a pyrolytic reforming process to raise its octane number. Sulfur dioxide is removed from stripping column 51 through line 58 and is re-introduced into tower 52. Sulfur dioxidel passes from the top of tower 52 in vapor form through line 59, compressor -60 and cooling and/or condensing coil 5i into storage tank 33 from which it is subsequently re-introduced into the process. l

It will be seen from the foregoing description that by means of a three-stage processthe advantages of counter-current extraction have been obtained. 'I'hus the material passing into separator I6 contains, in addition to fresh lubricating oil stock, fresh naphtha and a lubricating oil extract which has twice had its ramnate fractions removed. The saturated constituents of the naphtha, having a relatively high solvent power for oil, remove practically all of the more valuable lubricating oil constituents and prevent them from passing out oi' the process through line I1. In the second stage of the process, that is. in separator 38, the ratio of sulfur dioxide to naphtha has been raised by the removal of a highly olefinic portion of the naphtha through line I1 and by the introduction of the extract from the third stage of th'e process which is high in sulfur dioxide. The result is that an increased amount of the paraiiinic and naphthenic lubricating oil constituents appear in the raiiinate from this second stage of the process. In the third stage, that is, in separator 48 the sulfur dioxide-naphtha ratio is again increased, this time by the introduction of fresh liquid sulfur dioxide, and a maximum amount of the oleiinic constituents of the naphtha is removed and recycled to the second stage.

A special feature of my process resides in the fact that at one and the same time I am able to fractionate a lubricating oil stock into a relatively high grade and a relatively low grade fraction and fractionate an oleiinic naphtha into a high octane number fraction and a low .octane number fraction. In typical instances I can produce from 40 to 90% of an extract lubricating oil fraction having a viscosity-gravity constant (Industrial and Engineering Chemistry, volume 24, page 1371, December, 1932) from .01 to .07 lower than that of the original lubricating oil stock and from .01 to .03 lower than that of the rafiinate fraction produced by the use of liquid sulfur dioxide alone. Simultaneously I produce from 15 to 60% of an extract naphtha fraction having an octane number (National Petroleum News, June 4, 1930; page 35) from 3 to 20 points higher than that of the original naphtha stock. It will be readily comprehended that this proc.-

ess can be used on a variety of petroleum materials such as gas oil and lubricating oils, under a variety of operating conditions.

the gasoline boiling point range. 'I'he temperature of the extraction is preferably between 0 and 50 F., although much lower temperatures'and somewhat higher temperatures can be used if desired. Throughout most of the preferred temperature range the system should be held under pressure, but if it is desired to operate at low temperatures this can be done by partially exhausting at each stage of the process. The temperature of each stage can be varied by varying thepressure from point to point and/or by the use of heaters and/or coolers. It is also sometimes desirable to heat the various materials prior to or during the mixing steps and then to cool them to enhance separation into extract and raffinate fractions.

The olefinic naphtha used in my process may be a pressure distillate, particularly a pressure distillate from a vapor phase cracking process. Oleiinic gasolines, refined or unreiined, can also be used. It is generally advantageous, however, to use a cracked heavy naphtha, for instance, a naphtha boiling between 250 F. and 450 F. The use of a naphtha of this type increases the ease of separationof sulfur dioxide from the naphtha, lowers naphtha losses and increases the efiiciency of the naphtha fractionation since the low boiling constituents are in general already high in octane number. As one example of such a cracked heavy naphtha, I may use a vapor phase cracked naph- As a preferred embodiment, I treat the total lubricating oil fraction from um honing between 250 F. and 450 r. and containing approximately 52% olenes, 1% aromatics and 47% parailins and naphthenes.

In one modification of my invention I extract the naphtha initially with liquid sulfur dioxide and employ only the extract portion in my lubricating oil refining process. I may use a cracked heavy naphtha or other low boiling hydrocarbon mixture containing oleiinic hydrocarbons, such as cracked' gasoline or liquefied hydrocarbons recovered from cracking still gases. On treating such a naphtha with liquid sulfur dioxide at temperatures below the rniscibility ternperature. an extract is obtained which may be used directly in my lubricating oil fractionation process without elimination of the sulfur dioxide contained'in the naphtha extract. After the unsaturated hydrocarbon material has performed its function in the extraction of undesirable con-' stituents from the lubricating oil, it may be recovered and re-used, or it may be discharged from the process and used as a high octane number motor fuel or blended with other materials in the manufacture of such a motor fuel.

Although I prefer to use a counter-current process as described, it will be understood that a batch process in which the liquid sulfur dioxide.,

oleilnic material and lubricating oil stock are coagitated below the miscibility temperature or a batch process in which these materials are put into solution and then separated into raliinate and extract fraction by cooling can be used.

The principal requisite of the olefinic material used in my process is the presence of substantial amounts, preferably at least of an olefinic hydrocarbon or olenic hydrocarbons boiling below about 400 F. and preferably below 350 F. Higher boiling olenes are unsuitable.

Instead of using cracked naphtha I can obtain the same beneficial results insofar as the improvement of the lubricating oil stock is concerned by the use of pure olefinic hydrocarbons or mixtures of these. As examples, I may use ethylene,

propylene, butylene, or amylene or their mixtures as they occur naturally in cracking still gases. Using these low boiling olefnes has the advantage of permitting low operating temperatures without the use of sub-atmospheric pressures.

'I'he ratio of olenic hydrocarbon or naphtha to liquid sulfur dioxide will obviously vary with the type of material it is intended to extract and the desired degree of extraction. In generalfI prefer to use about one volume of oleiinic material to from 2 to 5 volumes of liquid sulfur dioxide but ratlos as low as one volume. of oleflnic material to 20. of sulfur dioxide show some advantage over liquid sulfur dioxide alone and ratios as high as one-to-one or even higher can be used under some conditions.

The ratio of the total volume of liquid sulfur dioxide and olefinic material to the volume of lubricating oil stock or other petroleum material ,to be extracted can be varied within wide limits but preferably between 1 volume of mixed solvent to 2 volumes of oil and 5 volumes of mixed solvent to 1 volume of oil.

Insofar as the simultaneous solvent fractionation of a. lubricating oil stock and an olefinic naphtha stock is concerned it will beunderstood that my invention is not restricted to the use of liquid sulfur dioxide but that other selective solvents such as methyl alcohol, acetone, aniline or liquid carbon dioxide can be used in place of liquid sulfur dioxide. These alternative solvents are, however, in one way or another generally inferior to sulfur dioxide.

Although I have describedmy invention in terms of certain specific embodiments thereof, it will be readily comprehended that numerous L'modifications fall within its scope and I do not wish to be limited except to the subject matter of the appended claims.

I claim:

1. In the solvent fractionation of a lubricating oil stock the steps which comprise mixing said vstock with a substantial amount of liquid sulfur dioxide and a substantial amount of a vapor phase cracked naphtha containing at least 25% olefins and separately recovering an extract fraction and a rafllnate fraction.

2. Steps according to claim l in which said naphtha is a heavy naphtha boiling between about 250 F. and about 450 F.

3. In the solvent fractionation of a lubricating oil` stock the steps which comprise mixing said stock with a substantial amount of liquid sulfur dioxide and a substantial amount of a vapor phase cracked naphtha containing approximately 52% olenes and separately recovering an extract fraction and a raffinate fraction.

4. Steps according to claim 3 in which said naphtha is a heavy naphtha boiling between about 250 F. and about 450 F.

5. In the solvent fractionation of a lubricating oil stock the steps which comprise mixing said stock with a substantial amount of liquid sulfur dioxide and a substantial amount of a solvent extract from a vapor phase cracked naphtha, said solvent extract containing at least about 25% olefins and separately recovering an extract fraction and a rainate fraction.

6. In the solvent fractionation of a lubricating oil stock the steps which comprise mixing said stock with a substantial amount of liquid sulfur dioxide and a substantial amount of a vapor phase cracked naphtha containing at least 25% oleflns oil stock the steps which comprise mixing said stock with a substantial amount of liquid sulfur dioxide and a substantial amount of a vapor phase cracked naphtha containing at'least 25% oleflns boiling below about 350 F. and separately recovering an extract fraction and a raffinate fraction.

8. In the solvent fractionation of a lubricating oil stock the steps which comprise mixing said stock with a mixed solvent comprising liquid sulfur dioxide and a vapor phase cracked naphtha containing at least about 25% olens, in a proportion between one volume of mixed solvent to two volumes of said stock and five volumes of mixed solvent to one volume of said stock, said mixed solvent comprising said sulfur dioxide and said vapor phase cracked naphtha in a proportiqn of one volume of said vapor phase cracked naphtha to from two to ve volumes of said liquid sulfur dioxide, and separately recovering an extract fraction and a raiinate fraction. 

